1. Field of the Invention
The present invention relates to a work station chair, and in particular, to a chair having a seat which can shift in response to different positions of a person working at a table or similar station which normally requires the person to lean forward in a working mode and to lean back in a rest position.
2. Description of the Prior Art
There have been many attempts to better design a seating arrangement for persons working at a desk or computer terminal. Such ergonomic chairs are described, for instance, in U.S. Pat. No. 4,650,249, issued Mar. 17, 1987 to Serber, and U.S. Pat. No. 4,738,487, issued Apr. 19, 1988 to Shalinsky et al.
In the Serber patent, a complicated body support system is illustrated which includes, amongst other things, an arcuate concave track system which allows the seat pan to slide through a concave arc. The track system is pivotally mounted to a base which leaves the seat pan quite unstable, unless the pivot is locked.
The Shalinsky et al patent includes a pivoting seat pan mounted to a stem which pivots at its base providing a convex arc for the forward tilting movement of the person sitting on the seat. This latter chair is satisfactory, but the radius of the arc is limited to the length of the stem from the base to the seat. The arc of movement, or tilt, is a function of the height of the person.
In the case of the Serber patent, it can be seen that when the seat pan slides forward, the center of gravity of the person moves forward past the pivot center causing the seat to tend to pivot forward to dump the load thereon. Unless the pivot is locked, the person will have to counteract this tendency.